1. Field of the Invention
The present invention relates to a tone generating apparatus and method for use in electronic musical instruments, such as a synthesizer, an electronic piano, an electronic organ and a single keyboard. More particularly, this invention pertains to a tone generating apparatus which repeatedly reads out tone wave data efficiently stored in a wave memory to thereby generate the associated musical tone.
2. Description of the Prior Art
Recently, development of acoustic instruments, such as a piano and an organ, into electronic instruments has become active, providing electronic musical instruments, such as an electronic piano and electronic organ. In addition, a synthesizer which generates tones with a unique timbre is realized as an electronic musical instrument.
These electronic musical instruments have a tone generating apparatus (tone generator) with an incorporated wave memory in which tone wave data is stored. The wave memory has multiple groups of tone wave data stored in association with respective timbres to permit generation of various timbres. One group of tone wave data consists of multiple pieces of tone wave data to generate a predetermined tone waveform.
In such a tone generating apparatus, when a predetermined timbre is specified operating a panel switch, for example, one group of tone wave data is selected from the multiple groups of tone wave data stored in the wave memory. Each tone wave data constituting the selected group is read out at a speed corresponding to the pitch specified by a key. The read-out tone wave data is reproduced into a tone waveform by a waveform generator, and it is output as a tone wave signal to an acoustic circuit. Upon reception of this tone wave signal, the acoustic circuit drives loudspeakers, a headphone or the like in accordance with the tone wave signal, thereby releasing a musical tone.
Because of the limited capacity of the wave memory, the conventional tone generating apparatus employs the art of compressing tone wave data before storing it in the wave memory.
For instance, a group of tone wave data of a musical tone having a certain timbre is generated as follows.
First, pulse code modulated (PCM) wave data which is to be original wave data (original data) is prepared. Then, two pieces of data with a predetermined length are consecutively extracted from the original data at an arbitrary position, the first half portion subjected to fade-in processing and the second half portion subjected to fade-out processing.
Next, the wave data having undergone the fade-in processing is mixed with the data having undergone the fade-out processing by performing an arithmetic operation (which is called "cross-fade mixing"). The cross-fade-mixed data serves as loop data which is to be repeatedly read out.
Then, data extending from the head of the original data to the middle of the extracted pieces of data is linked with the loop data to acquire a group of tone wave data for a certain timbre. The tone wave data group thus produced is stored in a wave memory.
The tone wave data group stored in the wave memory is first read out once from the head to the last portion to release the associated musical tone. Thereafter, only the loop data portion will repeatedly be read out to release the associated musical tone.
With the above arrangement, the tone generating apparatus can reproduce, with high fidelity, a complex and delicate sound included in the attack portion of a musical tone and can generate a musical tone of the sustaining portion with fewer pieces of tone wave data, thus ensuring data compression. Further, the execution of cross-fade mixing smooths where the attack portion of the musical tone and the repetitive-reading portion are linked, and smooths the link between the consecutive repetitive-reading portions as well.
However, the data of the attack portion of a musical tone consisting of a group of tone wave data prepared by the above method should at least amount to the aforementioned predetermined length (equal to the length of loop data) or greater. Preparation of tone wave data groups in accordance with various timbres, tone ranges, etc., therefore, would result in a vast amount of data.
In addition, it is necessary to provide a certain amount of tone wave data of the repetitive-reading portion (loop data) to avoid a cyclic uncomfortable sound which may result from an insufficient amount of tone wave data.
The conventional method of preparing, storing or reproducing a group of tone wave data requires a large-capacity wave memory, inevitably increasing the cost of the tone generating apparatus.